I've created a new web part in a sandbox solution. This web part has a custom string property called 'PetName'.

I'd expect to be able to set the initial value of this property in the .webpart file. While this works perfectly in a Farm solution, in a Sandbox solution it does not. The field shows in the web part properties on the UI, but it is blank. I am able to persist a value if I enter a value into the field and click OK.